2Rheumatology Research Center, Tehran University of Medical Sciences, Tehran, Iran

31. Rheumatology Research Center, Tehran University of Medical Sciences, Tehran, Iran 2. Department of Immunology, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran

Abstract

Twin studies have been considered as strong approaches in determining the cause of complex diseases with regard to identification of involvement of multigene, single genes, environmental factors, and possible relation between genetics and environment. The concordance observed among monozygotic (MZ) twins suggest involvement of genetic factors. Nonetheless, MZ twins demonstrate a rate of discordance in different characteristics like proneness towards diseases, despite virtually identical genetic background. Discordance has been suggestive of the involvement of environment, alongside with the genetic factors. AS a result, a bulk of studies has supported the hypothesis that environmental factors can impress the epigenetic construction and, therefore, influence on the disease susceptibility. Twin studies yield data about clinical courses and outcomes of diseases, in addition to the knowledge of genetics, epigenetics, environmental factors, and risk of disease development. To date, genome-wide association studies (GWASs) have reported that genomic variants responsible for only a number of autoimmunity twin cases and were unable to explain the disease discordance among MZ twins. With respect to exploration of epigenetic mechanisms in autoimmunity, discordant MZ twins have been attractive models and remarkably contributing tools. It is essential for the future studies to evaluate the genetic variants as well as epigenetic changes in large size of twin populations. This review discusses around the genetic and epigenetic lessons obtained from studies of twin cases.